This invention relates to improvements in a single facer.
Conventional single facers are shown in FIGS. 1 and 2.
In the conventional single facer shown in FIG. 1, there are provided an upper roll 1 having its external circumference formed into a corrugated shape and a lower roll 2 having the same external circumference as above in corrugated form. A sheet S.sub.1, of card-board fed into the meshing portion between said upper and lower rolls 1 and 2 is processed into a corrugated sheet S.sub.2. Subsequently, the corrugated sheet S.sub.2 is brought into contact with a pasting roll 7 so that a paste 8 can be applied to the top portion of the corrugated sheet S.sub.2 and, together with an another sheet S.sub.3 supplied from other direction, it is pressed and heated by the engaging point between a pressure roll 3 and the lower roll 2 until it is finished as a single-faced corrugated board S. FIG. 3a and FIG. 3b show an enlarged view of the pressing and heating step of the sheets 2 and 3 by the engaging point between the lower roll 3 and the pressure roll 3.
In this case, it is apparent that there occurs a change say, .delta. in axial distance between the pressure roll 3 and the lower roll 2 in the process of engagement from FIG. 3a to FIG. 3b. Namely, as the lower roll 2 makes one rotation, there occurs as many vibrations as the number of the circumferential teeth between the lower roll 2 and the pressure roll 3. Therefore, these vibrations cause noises and in the case of a low-quality sheet, it tends to be damaged at the engaging point between the lower roll 2 and the pressure roll 3 in common practice under the present circumstances.
FIG. 2 shows also an another conventional example disigned to prevent the generation of the aforesaid vibrations. Namely, in place of the pressure roll 3 shown in FIG. 1, there is provided a pressure member 10 in a position facing the lower roll 2 as shown in FIG. 2, said pressure member having a diameter or a curved surface equal to, or a little larger than, the diameter of the lower roll 2 so that there occurs no change in distance between the pressure member 10 and the lower roll 2 from an engaging point A to another engaging one B, as shown in FIG. 4.
The pressure member 10 has a curved surface of a length larger than the distance l between the teeth of the lower roll 2 and the pressure member 10 is pressed against the lower roll 2 in order to keep the sheet S.sub.3 and the corrugated sheet S.sub.2 in close contact so that, in the process of the engaging point A to B shown in FIG. 4, a contact portion C between the sheet S.sub.3 and the corrugated one S.sub.2 is subjected to frictional force between the sheet S.sub.3 and the pressure member 10. Under such circumstances, the sheet S.sub.3 does not advance to the same extent as the amount of progress of the corrugated sheet S.sub.2 with the result that there occurs a relative lag between both until the contact portion C becomes separated as a conventional drawback which has heretofore been common in practice.
At the same time, the aforesaid separation is sure to take place in the conventional example shown in FIG. 1. Namely, while the delivery of the required single-faced corrugated board S is to be accomplished by pressing force of the pressure roll 3 and the lower roll 2 against the rotation or resistance of inertia of a preheating roll 17 and a paper-winding roll (not shown), said pressing force is lowered for the prevention of cracking of said sheet S.sub.3 so that said contact portion C tends to be stripped or separated. In like manner, frictional force is usually lowered owing to the same phase of amplitude in the proximity of common vibration point at the lower roll 2 and the pressure roll 3. As the result, there occurs a difference in relative speed between the corrugated sheet S.sub.2 and the sheet S.sub.3 until said contact portion C becomes likewise separated.